JP2005214115A - Egr system for diesel engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To secure optimum EGR amount in accordance with an operating condition without complicating piping around an engine, in the diesel engine having a plurality of cylinders. <P>SOLUTION: This invention is applied to the diesel engine which has the plurality of cylinders and in which an exhaust manifold 30 is provided with a variable throttle mechanism 33 and each of the cylinders has variable valve systems 15, 17 capable of changing opening/closing timing of an intake valve 7 and an exhaust valve 8. In accordance with increase in required EGR amount, an overlap period of an exhaust valve opening period and an intake valve opening period is controlled to be shortened, and an opening of the variable throttle mechanism 33 is controlled to be reduced. For example, a load and engine speed are detected, and the overlap period and the opening of the variable throttle mechanism 33 are controlled in accordance with the required EGR amount in an operating range at the detected load and engine speed. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to an EGR system for a diesel engine having a plurality of cylinders.

  The EGR that reuses the exhaust gas for combustion introduces the exhaust gas in the exhaust pipe to the intake pipe once through the EGR pipe, mixes with the intake air and supplies it to the combustion chamber, and the exhaust gas after combustion. There is an internal EGR in which a part is left in the combustion chamber or is added back to the combustion chamber from the vicinity of the exhaust port.

The engine having the internal EGR is a gasoline engine, but an exhaust throttle valve is provided in the exhaust pipe, and the opening of the throttle valve is reduced in an operation region where a large amount of EGR is required. Some engines have been realized (see Patent Document 1).
Japanese Patent Laid-Open No. 5-86908.

  In the external EGR, an EGR pipe for guiding a part of the exhaust gas from the exhaust pipe to the intake pipe is required, the piping structure around the engine is complicated, and the manufacturing and assembling costs are also increased. Further, since the temperature of the exhaust gas decreases while passing through the EGR pipe, the sulfur content in the fuel is precipitated as sulfate, which adversely affects the engine durability.

  In the internal EGR provided with a throttle valve in the exhaust pipe, when the EGR amount is increased according to each operation region by adjusting the opening degree of the exhaust throttle valve, the EGR amount is immediately increased in response to a sudden change in operating conditions. It can be difficult. That is, the response of EGR control may be slow.

(Object of invention)
An object of the present invention is to provide a variable throttle mechanism in an exhaust passage in a diesel engine having a plurality of cylinders to change and adjust an exhaust cross-sectional area, and simultaneously change and adjust an overlap period between an exhaust valve opening period and an intake valve opening period. By doing so, a desired internal EGR amount can be secured quickly and accurately in accordance with each operation region.

  In order to solve the above-mentioned problem, the invention according to claim 1 of the present application is provided with a plurality of cylinders and a variable throttle mechanism in the exhaust collecting portion, and each cylinder has a variable motion capable of changing the opening and closing timings of the intake valve and the exhaust valve. A valve device is provided, and the overlap period between the exhaust valve opening period and the intake valve opening period is shortened and the opening degree of the variable throttle mechanism is controlled to be small as the required EGR amount increases. It is an EGR system of a diesel engine.

  According to a second aspect of the present invention, in the EGR system of the diesel engine according to the first aspect, the load and the engine speed are detected, and an overlap is detected according to the required EGR amount in the operation region at the detected load and the engine speed. Control period and opening of variable throttle mechanism.

  According to a third aspect of the present invention, in the EGR system of the diesel engine according to the first aspect, when the cooling water temperature sensor is provided and the engine cold state is detected by the cooling water temperature sensor, the opening degree of the variable throttle mechanism And the overlap period is controlled to be 0 or negative.

  According to a fourth aspect of the present invention, in the EGR system of a diesel engine, a variable valve that includes a plurality of cylinders and a variable throttle mechanism in an exhaust collecting portion, and each cylinder can change the opening and closing timings of an intake valve and an exhaust valve. When the required EGR amount is greater than or equal to a predetermined value, the opening of the variable throttle mechanism is minimized, and the valve closing timing of the exhaust valve is delayed until the timing when the exhaust gas recirculates into the combustion chamber during the intake stroke.

(1) By adjusting the exhaust cross-sectional area by the variable throttle mechanism provided in the exhaust collecting portion and adjusting the overlap period between the exhaust valve opening period and the intake valve opening timing, the internal EGR is set according to the required EGR amount in each operation region. Since the amount (residual exhaust gas) is controlled, piping such as the EGR pipe can be omitted compared to the external EGR, so that the piping around the engine can be simplified and the cost can be reduced. Compared to the internal EGR that adjusts the internal EGR amount, the EGR amount can be adjusted quickly and accurately as necessary.

(2) In a diesel engine having a plurality of cylinders, a variable throttle mechanism is arranged in the exhaust collecting portion, and the exhaust system pressure of each cylinder is collectively controlled, so that a variable throttle mechanism is arranged for each cylinder. The parts cost can be reduced and the assembly can be simplified. Further, since only one variable throttle mechanism needs to be controlled, the control is easy.

(3) When the engine load and the engine speed are detected and the overlap period and the opening of the variable throttle mechanism are controlled according to the required EGR amount in the operation region at the detected engine load and engine speed, the actual operation is performed. The amount of EGR can be accurately adjusted according to the situation, and EGR control can be performed without waste.

(4) When the engine cold state is detected by the coolant temperature sensor and the opening of the variable throttle mechanism is minimized while the engine is cold, and the overlap period is controlled to be 0 or negative, the engine cold start is started. Immediately after that, a large amount of EGR can be automatically secured, and the engine cold start performance is improved.

(5) When the required EGR amount is greater than or equal to the predetermined value, instead of minimizing the opening of the variable throttle mechanism and shortening the overlap period, the exhaust valve is recirculated into the combustion chamber during the intake stroke instead of closing the exhaust valve. If it is controlled so as to be delayed until the time to start, not only the exhaust gas in the combustion chamber but also the exhaust gas in the vicinity of the exhaust collecting portion can be recirculated to the combustion chamber, and the EGR can be controlled without controlling the opening timing of the intake valve. Can be increased.

[First Embodiment of the Invention]
FIG. 1 is a schematic view of a diesel engine to which an EGR system according to the present invention is applied. Although only one cylinder is shown, it is a multi-cylinder diesel engine, and other cylinders are omitted. The combustion chamber 1 of the cylinder is surrounded by the cylinder 2, the top wall of the piston 3, and the combustion chamber forming surface of the cylinder head 5. The cylinder head 5 has an intake hole 7 and an exhaust hole 8 that open to the combustion chamber 1. And a fuel injection valve 9 is mounted. The intake valve 10 disposed in the intake hole 7 is linked to the intake valve variable valve device 15, and the exhaust valve 11 disposed in the exhaust hole 8 is linked to the exhaust valve variable valve device 16. The variable valve operating devices 15 and 16 are both connected to the engine controller 20 so that the opening / closing timings of the valves 10 and 11 can be independently changed and adjusted by commands from the engine controller 20.

  The intake holes 7 are gathered in an intake manifold 22 via an intake passage 21 of each cylinder, and the intake manifold 22 is connected to an air intake device 26 such as an air cleaner via an intake cooler 23 and an intake pipe 25. An intake flow sensor 27 is disposed in the middle of the intake pipe 25, and the intake flow sensor 27 is connected to the engine controller 20.

  The exhaust holes 8 are collected in an exhaust manifold (exhaust collecting portion) 30 via an exhaust passage 29 of each cylinder, and the exhaust manifold 30 is connected to an exhaust muffler 31 and the like. The exhaust manifold 30 is provided with an exhaust variable throttle mechanism 33 that changes and adjusts the exhaust cross-sectional area of the exhaust collecting portion. The exhaust variable throttle mechanism 33 is connected to the engine controller 22, and its opening degree is determined by a command from the engine controller 22. Can be changed and adjusted.

  As described above, the flow sensor 27 and the load sensor 41 and the engine speed sensor 42 are connected to the input portion of the engine controller 20. The load sensor 41 is connected to, for example, a throttle device (accelerator device) 44. It connects, detects the opening degree (fuel injection amount) of a throttle lever (or accelerator lever), and inputs it into the engine controller 20 as a load. The engine rotation sensor 42 is disposed on the crankshaft 45, for example, detects the crankshaft rotation speed, and inputs it to the engine controller 20 as the engine rotation speed.

  The engine controller 20 incorporates a CPU having storage means, calculation means, and the like. The storage means stores the required EGR amount in each operation region determined by the torque and the engine speed, and each requested EGR. The overlap period and the opening degree of the variable throttle mechanism 33 (exhaust throttle opening degree) calculated in advance so as to correspond to the amount are stored as a map. That is, when the detected load and the engine speed are input, the engine controller 20 reads the overlap period and the exhaust throttle opening corresponding to the required EGR amount based on the map, and both the variable valve gears 15, 16 and the variable aperture mechanism 33 are programmed to issue commands.

  FIG. 2 shows a state in which the open periods of the intake valve 7 and the exhaust valve 8 overlap each other, and both the intake valve 10 and the exhaust valve 11 are open.

  FIG. 3 is a diagram showing changes in the overlap period that is controlled to be shortened and extended, where E is the exhaust valve lift, S is the intake valve lift, and the period OL1 formed by the solid lines E1 and S1 is the reference overshoot. The lap period, the period OL2 formed by the imaginary lines E2, S2 is a shortened overlap period, and the period OL3 formed by the broken line E3-S3 is an extended overlap period. In any of the overlap periods OL1, OL2, and OL3, the intake valve opening timings θS1, θS2, and θS3 and the exhaust valve closing timings θE1, θE2, and θE3 are generally symmetrical with respect to the top dead center (TDC).

  The upper shortening overlap period OL2 is a state in which the exhaust valve closing timing advances from θE1 to θE2 and the intake valve opening timing is delayed from θS1 to θS2 with respect to the reference overlap period OL1. Conversely, the extended overlap period OL3 is a state in which the exhaust valve closing timing is delayed from θE1 to θE3 and the intake valve opening timing is advanced from θS1 to θS3 with respect to the reference overlap period OL1.

[Setting of overlap period and opening of variable throttle mechanism]
FIG. 4 is a diagram showing the relationship between the overlap period and the EGR amount. When the overlap period is shortened from the reference period OL1 to, for example, the period OL2, the EGR amount increases abruptly. It is shown that the EGR amount decreases when the reference period OL1 is extended to the period OL3.

  FIG. 5 shows an example of the control of the overlap period and the exhaust throttle opening according to the present invention with respect to the change of the operation region. As the change of the operation region, the engine speed is applied to the horizontal axis and the torque (load) is applied to the vertical axis.

  In FIG. 5, a region A1 is a rated operation region with a high torque (high load) and a high rotation speed. Since the required EGR amount is small in this region A1, the overlap period is long (OL3 in FIG. 3), and the exhaust throttle The opening degree is set to be large, and the EGR amount can be suppressed to a small value.

  Region A2 is an operating region with low torque (low load) and low rotational speed, such as idling. In this region A2, the required EGR amount is very large, so the overlap period is short (OL2 in FIG. 3) and the exhaust throttle The opening degree is set to be small, so that an extremely large EGR amount can be obtained.

  Region A3 is an operation region with medium torque (medium load) and medium rotation speed. In this region A3, the required EGR amount is large to some extent, so the overlap period is set short (OL2 in FIG. 3). The throttle opening is set to be large, and a certain amount of EGR can be obtained only by the effect of shortening the overlap period.

  Region A4 is an operation region of high torque (high load) and medium rotation speed. In this region A4, the required EGR amount is considerably low due to the high torque, so the overlap period is long as in region A1 (see FIG. 3 OL3), the exhaust throttle opening is set to be large, and the EGR amount can be suppressed to a small value.

  The region A5 is a low torque (low load) and high rotation speed operation region. In this region A4, the required EGR amount is considerably large due to the low torque, so the overlap period is short as in the region A2 (FIG. 3 OL2), the exhaust throttle opening is set to be small so that a considerably large EGR amount can be obtained.

(EGR control)
In FIG. 1, when a detected load and a detected engine speed are input to the engine controller 20 from the load sensor 41 and the engine speed sensor 42 during engine operation, based on the map previously written in the storage means of the engine controller 20. The overlap period and the exhaust throttle opening corresponding to the required EGR amount in each operating state are read, and commands are issued to the variable valve mechanisms 15 and 16 and the variable throttle mechanism 33 according to the read values, The variable valve mechanisms 15 and 16 and the variable throttle mechanism 33 are adjusted to the overlap period based on the map and adjusted to the exhaust throttle opening.

  Specifically, as described with reference to FIG. 5, when the engine is operated in the low torque and low rotation speed region A2 as in idling, the overlap period is shortened and the exhaust throttle opening is reduced to be considerably large. Increase EGR amount to value.

  In the case of rated operation with high torque and high rotation speed as in region A1, the overlap period is lengthened and the exhaust throttle opening is increased, thereby suppressing the EGR amount to a very small value.

  When the vehicle is operated at medium torque and medium rotation speed as in the region A3, the overlap period is shortened and the exhaust throttle opening is increased to obtain a somewhat large EGR amount.

  As in the area A4, when operating at a high torque and a medium rotational speed, the torque is large. Therefore, as in the rated operation area A1, the overlap period is lengthened and the exhaust throttle opening is increased. In addition, the EGR amount is suppressed to an extremely small value.

  When operating at a low torque but at a high speed as in the region A5, the overlap period is shortened and the exhaust throttle opening is reduced to obtain a considerably large EGR amount.

[Second Embodiment of the Invention]
As shown by the phantom line in FIG. 1, a cooling water temperature sensor 61 for detecting the temperature of the cooling water is arranged in the cooling water passage 62 and the like, and a cooling water temperature below a certain temperature is detected when the engine is cold. In such a case, the opening of the variable throttle mechanism 33 is set to the minimum and the overlap period is set to be short (OL2 in FIG. 3).

  Therefore, at the time of engine cold start, the exhaust throttle opening is minimized and the overlap period is shortened (OL2 in FIG. 3), so that an extremely large EGR amount can be obtained and the temperature of the gas in the cylinder is raised. Thus, a cold start can be performed.

[Third Embodiment of the Invention]
In FIG. 4, the relationship between the overlap period and the EGR amount (residual gas ratio) indicates that the EGR amount (residual gas ratio) decreases as the overlap period becomes longer until a certain overlap period OL4. In each embodiment, the decrease in the EGR amount is used. However, with the opening of the variable exhaust throttle mechanism 33 shown in FIG. 1 being minimized, the overlap period is a fixed period as shown by the phantom line in FIG. If longer than OL4, the exhaust gas in the exhaust passage recirculates to the combustion chamber, causing a phenomenon that the residual gas increases rapidly.

  In this embodiment, when the required EGR amount is a certain value or more, instead of shortening the overlap period as in the first and second embodiments described above, the exhaust valve is closed as shown by the phantom line in FIG. The EGR amount is increased by largely extending the timing to the crank angle θE4 within the intake stroke and maintaining the opening of the exhaust variable throttle mechanism 33 to a minimum.

  That is, the present embodiment uses the recirculated exhaust gas as the internal EGR by extending the overlap period from the overlap period S4 of FIG. 4 while keeping the exhaust throttle opening at a minimum.

  FIG. 8 is a diagram showing changes in the volume and pressure of the combustion chamber, where the solid line is the normal operating state, and the portion indicated by the phantom line is the exhaust throttle opening is minimized and the overlap period is the period OL4 in FIG. It is a change when it is larger than that and extended to the reflux possible range.

  The present invention is applicable to various industrial large and small diesel engines, but is also applicable to vehicle diesel engines.

It is the schematic of the diesel engine which applies the EGR system by this invention. It is the schematic of the diesel engine in an overlap period. It is a figure which shows the change of the exhaust valve lift and the intake valve lift with respect to the change of a crank angle. It is a figure which shows the change of the EGR amount with respect to the change of an overlap period. It is a figure which shows the control content of the overlap period and exhaust throttle opening according to this invention with respect to the change of an engine torque (engine load) and an engine speed. It is a figure which shows the exhaust valve lift and intake valve lift in another EGR system of this invention. FIG. 7 is an engine cycle diagram showing changes in the volume and pressure of a combustion chamber corresponding to FIG. 6.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Combustion chamber 5 Cylinder head 7 Intake hole 8 Exhaust hole 10 Intake valve 11 Exhaust valve 15 Intake valve variable valve device 16 Exhaust valve variable valve device 20 Engine controller 30 Exhaust collecting part 33 Exhaust variable throttle mechanism 41 Load sensor 42 Engine speed sensor 61 Cooling water temperature sensor

Claims (4)

A plurality of cylinders and a variable throttle mechanism in the exhaust collecting portion, each cylinder is provided with a variable valve operating device capable of changing the opening and closing timing of the intake valve and the exhaust valve,
The EGR of a diesel engine is characterized in that the overlap period between the exhaust valve opening period and the intake valve opening period is shortened according to the increase in the required EGR amount, and the opening of the variable throttle mechanism is decreased. system.   The load period and the engine speed are detected, and the overlap period and the opening of the variable throttle mechanism are controlled in accordance with the required EGR amount in the operation region at the detected load and engine speed. EGR system for diesel engines.   A cooling water temperature sensor is provided, and when the engine cold state is detected by the cooling water temperature sensor, the opening of the variable throttle mechanism is minimized and the overlap period is controlled to be zero or negative. The EGR system for a diesel engine according to claim 1. A plurality of cylinders and a variable throttle mechanism in the exhaust collecting portion, each cylinder is provided with a variable valve operating device capable of changing the opening and closing timing of the intake valve and the exhaust valve,
A diesel engine characterized in that when the required EGR amount is greater than or equal to a predetermined value, the opening of the variable throttle mechanism is minimized and the valve closing timing of the exhaust valve is delayed until the time when the exhaust gas recirculates into the combustion chamber during the intake stroke. EGR system.

Images